1. Field of the Invention
The present invention relates to a heating control apparatus adaptable to a wide variety of uses but having particular utility when incorporated in the controls of a kiln or the like, and more particularly to a heating control apparatus that is inexpensive to manufacture and which has improved performance relative to prior art devices, particularly with respect to providing for the easy one-step operation of the kiln, the apparatus providing enhanced operational characteristics for the kiln under a variety of time, temperature and load conditions.
2. Description of the Prior Art
One of the hobbies most enjoyed by arts and crafts enthusiasts is that of ceramic crafts. With the advent of improved instruction techniques and the development of relatively inexpensive materials and equipment, this once quite exclusive hobby is now enjoyed by large numbers of individuals of all levels of artistic and creative ability.
However, whether in the hobby or in the industrial area, artisans practicing in the ceramic arts agree that one of the most important considerations in the firing of a ceramic piece is to control the low fire heating stage to prevent the piece from becoming damaged. Those skilled in the ceramic arts recognize, in firing a piece of ceramic material, that a hazard of damage or explosion exists if heat energy is imparted to the piece in too rapid a fashion. As heat energy is applied to an unprocessed piece of ceramic material, water in the form of steam and other gases are driven off from the piece. It has long been known if excessive heat energy is applied too early during firing, gases and other vapor which would have escaped from the piece are caused to be trapped internally of the piece. This entrapment of the gas is caused by the expansion of the external surface of the piece in such a manner that substantially all the surface pores, which would have permitted the escape of the gases, are closed off. If this situation is allowed to continue, the heat energy which continues to be imparted to the piece causes the expansion of the gas and other vapors internally of the piece until such time as the expanding gas destroys the piece by fracturing it, or, in aggravated situations, causing it to explode. In this latter situation, there is an attendant risk of injury to persons in the area.
Manufacturers of kilns and artisans have approached the problem of controlling the heat imparted to a ceramic piece during firing by directing their attention to improving the controls which deactivate the kiln after selected periods of time and which control the rate of heat input to the kiln. The controls that are adapted to influence the rate of heat input in the kiln are of two general types, manual and electronic. Manual controls have significant shortcomings because they require repeated trips to the kiln. Electronic controls are expensive, sensitive to heat energy produced by the kiln and are not generally responsive to varying firing loads.
Although there have been some significant advances in producing kilns for home and industrial use which give the individual craftsman improved control with respect to the amount of heat energy imparted to a ceramic piece during all stages of kiln operation, the improvements have only been marginally satisfactory. As a consequence, artisans of all levels of artistic ability have continued to seek a kiln having one-step controls which permit them to preselect the correct low fire and high fire load conditions for the ceramic piece which will be fired, whereby the kiln will automatically, after a predetermined period of time, switch from the low fire stage to the high fire stage to permit the efficient processing of the ceramic piece.
Therefore, it has long been known that it would be desirable to have an improved heating control apparatus for kilns or the like which is adapted for both home and industrial use, which has improved control characteristics and which otherwise performs in a highly advantageous manner under variable load conditions.